1. Field of the Invention
The present invention relates in general to a system and method for a call assignment in a mobile communication system, and in particular, to a system and method of controlling an assignment of a reverse call in a mobile communication system.
2. Description of the Related Art
In a mobile communication system, upon a request for the establishment of a call between an MS (Mobile Station) and a BS (Base Station), the call is assigned based on the availability of radio channel resources. Therefore, a call cannot always be assigned. While a dedicated line is assigned to a terminal in wired communications, in wireless communications a call cannot be assigned to an MS when all radio resources available to the BS are in use. Handoff is also a consideration due to the mobility of the MS in the mobile communication system.
Existing 2nd Generation (2G) Code Division Multiple Access (CDMA) systems primarily provide voice service. The voice service is provided via FCHs (Fundamental Channels) on forward and reverse links. The Forward link is in the direction from the BS to the MS. The reverse link is in the direction from the MS to the BS.
To satisfy growing user demand for various services, systems that also provide data service have been proposed and standards are being developed to provide global use of the data service. CDMA2000 is one of the proposed systems. It uses the Fundamental Channel (FCH), a Pilot Channel (PCH), and a Supplemental Channel (SCH). The SCH delivers data at a high rate, e.g., Radio Configuration3 (RC3) 9.6, 19.2, 38.4, /76.8, /153.6, and 307.2 Kbps. If a user is assigned an FCH at 9.6 Kbps and an SCH at 153.6 Kbps in RC3, data can be transmitted at a high rate of 163.2 Kbps.
For the CDMA2000 system, transmission power is determined according to the Frame Error Rate (FER) of the FCH. The transmission power of the PICH is determined such that an appropriate FER is maintained for the FCH. The transmission power of the FCH and the SCH is the product of the PICH transmission power and predetermined constants. Hence, the transmission power of an MS is calculated usingtransmission power=pilot transmission power×(1+FCH_offset+SCH_offset)where the FCH_offset and the SCH_offset are the offsets of the FCH and SCH, respectively with respect to the PICH. The FCH-offset and SCH_offset are constants that vary with channel type, data rate, RC, and coding.
The CDMA mobile communication system basically supports soft handoff and softer handoff. Soft handoff is means communication with a new BS without interrupting communication with an old BS. Softer handoff is handoff between sectors within a cell, with continuity of a call. Softer handoff is simpler to implement than soft handoff. For example, a plurality of channel elements (CEs) are required during a soft handoff, but a single CE is sufficient during a softer handoff.
As stated, CDMA has evolved from the 2G system to the CDMA2000 system with the goal of providing a high-rate data service. Although, the CDMA2000 system initiated the high-rate data service some time ago, little research has been conducted to support efficient provisioning of the high-rate data service. Moreover, studies on the reverse link have been confined to voice service, particularly to call assignment control, power control, soft/softer handoff, and sector capacity analysis. However, as high-rate data transmission as well as voice service is carried out on the reverse link, issues that require consideration have emerged.
First of all, there is a need for a call assignment control technique to ensure quality of the high-rate data service without impairing the quality of the existing voice service. Soft/softer handoff must be performed reliably so that a user can receive the high-rate data service using an FCH and an SCH simultaneously, while handoff. Unlike the voice service, the high-rate data service requires high MS power. Thus, as an MS moves away from a BS, the MS's transmission power may be insufficient. As described, reverse power control is based on a reverse FCH (R-FCH). For high-rate data service, the MS uses a lot of a sector's capacity. Thus, a related power control leads a rapid increase in load and decreases the communication quality of other MSs.